Definitions: Unless expressly stated otherwise, laser beam, light beam, partial beam or beam does not refer to an idealized beam of geometrical optics, but to a real light beam, such as a laser beam with a Gaussian profile or a modified Gaussian profile or a top-hat profile which does not have an infinitesimally small, but rather an extended beam cross section. Top-hat distribution or top-hat intensity distribution or top-hat profile refers to an intensity distribution that can be described at least in one direction substantially by a rectangular function (rect (x)). Real intensity distributions that deviate from a rectangular function in a percent range or have sloping edges shall also be designated as a top-hat distribution or a top-hat profile.
A device of the aforementioned type is known from DE 10 2007 001 639 A1. In the device described therein, a plurality of laser light sources in multi-mode operation is provided. Their laser beams are intermixed in a rod-shaped homogenizer and superimposed on themselves. They are thereafter converted by collimating and focusing lenses into a linear intensity distribution in a working plane.
Such laser systems with a line focus and a homogeneous intensity distribution are known in the prior art from many technical applications with multi-mode laser sources and are currently in use. The physical reason therefor is that the radiation from multimode lasers can be divided into beams, wherein these beams can be later optically overlapped and mixed or homogenized virtually without any interference fringes. As a result, homogeneous light fields with almost any geometry can be created from multi-mode laser sources. Technically used are in particular rectangular and linear light fields with rectangular top-hat intensity distribution.
It turns out to be problematic that fundamental mode laser are not suitable for the homogenization and overlap described in DE 10 2007 001 639 A1. Fundamental mode laser are currently used in most cases with the familiar point focus. In a few exceptional cases, beam shaping optics is used with fundamental mode lasers, which however operates according to physically principles different from beam shaping optics used with multimode lasers: The radiation of fundamental mode lasers is very coherent, producing strong interference fringes when overlapped with itself. The beam shaping used with fundamental mode lasers is therefore according to the prior art produced by diffraction effects, meaning diffractive or coherent deformation of the wave front.
The problem underlying the present invention is to provide a device of the aforementioned type which can produce a comparatively homogeneous linear intensity distribution in a working plane in spite of the use of fundamental mode lasers.